1. Field of the Invention
The present invention relates to an imaging unit used in an ophthalmologic imaging apparatus.
2. Description of the Related Art
A fundus camera that performs positioning and focusing by illuminating a fundus with visible light or infrared light, and performs fundus imaging with a strobe light is used conventionally in applications such as fundus diagnosis, diabetes medical examination, etc. In an application of a physical examination especially, a non-mydriasis fundus camera that is capable of imaging without using a mydriatic agent is mainly used. A non-mydriasis fundus camera like this avoids miosis of a subject's eye through the use of infrared light for illumination.
A single-lens reflex type camera may be used for still-image imaging of a fundus camera. In recent years, single-lens reflex digital cameras that form electronic images using image sensing devices such as CMOS and CCD etc. have been used for fundus imaging more often. A single-lens reflex digital camera that has a live view function which provides continuous display of images onto a liquid crystal display on the back surface of an image sensing device has also been released to the market.
However, commercially available single-lens reflex digital cameras are provided with a characteristic to filter out infrared light for the purpose of removing the influence of infrared light on color reproduction. An infrared-cutting characteristic has been realized by installing an optical member that reflects or absorbs infrared light at the front of an image sensing device.
Therefore, for infrared monitor observation in a non-mydriasis fundus camera, the live view function of a single-lens reflex digital camera was not able to be used as it was.
In view of the above situations, the present applicant, by removing an infrared-cutting characteristic from a single-lens reflex digital camera, have proposed an imaging unit for a fundus camera that can be used for observation by utilizing the live view function at the time of non-mydriasis.
However, there are a plurality of models of fundus cameras to which such an imaging unit is attached, and due to the application difference etc., optical characteristics or light source characteristics may vary, and therefore it may be necessary to prepare an imaging unit that is compatible with different fundus cameras. For example, due to differences in the optical system configuration, depending on the model of the fundus camera, there was a case where an image is formed on an image sensing device of an imaging unit with the vertical and horizontal directions inverted.
In this case, when performing observation using live view, in some fundus camera models, a normal image is displayed on its back surface, and in other models, a vertically and horizontally inverted image is displayed. If a vertically and horizontally inverted image is displayed in live view, position adjustment (alignment) for imaging will be very difficult.
In Japanese Patent Laid-Open No. 10-179523 (hereinafter, Patent Document 1), disclosed is a technique related to a digital camera that displays a live view of vertically and horizontally inverted images when attached to a fundus camera, and returns a live view display to a normal display when removed from the fundus camera. However, in Patent Document 1, a technique that changes a display direction of a live view depending on a model of a fundus camera to which the digital camera is attached is not mentioned.
Although a xenon tube is mainly used as an imaging light source of a fundus camera, luminance increase of a white LED has progressed recently, and an example in which a white LED is adopted as an imaging light source has also been found. However, a xenon tube differed in spectral characteristic as a light source greatly from a white LED, and white balance correction and color correction corresponding to each of the light sources were required in an imaging unit side.
In the latest digital cameras, there are also ones in which aberration correction of an imaging lens, such as light falloff at edges, chromatic aberration of magnification, distortion etc. is possible. A fundus camera is influenced especially by light falloff at edges, because the camera takes an image of a fundus of human-eyes that is not flat but spherical, and an imaging light source is used for imaging, and light distribution unevenness of the imaging light source is always included in the taken image, and so on. Since an imaging field angle and an optical characteristic differed depending on a model of a fundus camera, in the case of correcting optical aberration such as light falloff at edges, there was the necessity of preparing an imaging unit that was made to have corrective parameters corresponding to a model of a fundus camera.
As stated above, depending on the model of the fundus camera, an imaging unit corresponding to the direction of a live view display, a wavelength characteristic of a light source, or an optical characteristic such as light falloff at edges was needed to be prepared in each case, and this had become a cost up factor during production or management. Likewise, to a user who uses a plurality of sets of fundus cameras such as in medical examination applications, there was the necessity of operating an imaging unit fixedly in association with a model of a fundus camera, and this had forced disadvantages on a user in respect of management.